Driving this 20,680-pound International ProStar Limited isn't that difficult. You step on the weighty clutch, jam the 13-speed Fuller transmission with shifter-selectable low and high ranges into first, let out the clutch, upshift at about 1500 rpm -- redline is 2000 on the 912-cubic-inch Cummins turbo-diesel -- and keep it between the lines with reasonably tight steering until the 225 gallons of fuel are used up, or for about 1800 miles, assuming a typical 60,000-pound load. In fact, the hardest thing about being a ProStar driver might be choosing between the Shrimp & Cheddar Grits and the Pancho Villa's Burrito at the Flying J truck stop.

In Pictures: 2007 International Prostar Limited

Okay, it's a bit tougher than that. But the most earnest thinking in trucking these days isn't behind the wheel; it's under the hood and cab, where the hauling industry is being forced by government regulations to clean up its gases, burritos notwithstanding. The $186,240 ProStar pictured here -- fitted with a diesel-soot-trapping filter, fuel-saving auxiliary-power system, cost-saving and maintenance-easing design, and wind-cleaving body -- is the rig of the future.

2007 International Prostar Limited
The HighsThe Lows
Takes 60,000 pounds where you need it, drives better than an Excursion, 1800 miles per fill-up.Has parallel-parking issues, requires a special license, about $700 per fill-up.

Its arrival comes none too soon. Despite tough emissions laws for cars, heavy diesel trucks roar down the interstates trailing charcoal-black. Nearly all the 3.51 million trucks on our highways defined by the U.S. Department of Energy as Class 8 (above 33,000 pounds gross vehicle weight) spew untreated diesel exhaust. Gasoline engines burn cleaner, but they can't match the efficiency or durability of a diesel when cruising the highway, so all big rigs run oil burners. The heavy-truck fleet generates more than twice as many carcinogenic soot particulates as the roughly 200 million light vehicles on the road combined, according to a 1998 Environmental Protection Agency study. Until this year, heavy trucks were not even required to recycle or filter crankcase blow-by, a requirement on U.S.-sold passenger cars since 1963.

Emissions technology long familiar to car engineers is filtering into heavy trucks as the regulatory noose tightens around cast-iron workhorses such as the ProStar's Cummins ISX-series inline-six. Each of the ISX's 5.39-inch-diameter pistons moving a distance of 6.65 or so inches displaces more volume than a base Honda Accord's four-cylinder, and at 2940 pounds, the ISX weighs almost as much as an Accord itself. A low-revver twisting out 1550 pound-feet of torque, the ISX is relatively stingy with fuel -- expect a fully laden ProStar to deliver up to 8 mpg, says International -- but has the murderously high cylinder temperatures that spawn oxides of nitrogen (NOx). It also generates copious amounts of the ultra-fine carbon granules called particulates.

In 2002, the EPA drastically tightened the NOx standard, which the big Cummins meets with exhaust-gas recirculation. A portion of the 1300-degree-Fahrenheit exhaust gas is routed through a water-to-air intercooler that drops it to 400 degrees, whereupon it is plumbed to the intake to reduce combustion temps and cut NOx.

In 2006, the EPA phased in ultra-low-sulfur diesel fuel and also went after particulate matter, reducing the allowable soot from a heavy truck by 90 percent. Underneath the ProStar is a mammoth steel canister where soot goes to die. Inside, a porcelain filter traps particulates in small dead-end pits and incinerates them into carbon dioxide with the attached diesel-fuel burner. After 200,000 to 400,000 road miles, depending on the duty cycle, the filter is removed and cleaned of residual oil ash.

From the ProStar's exhaust stack comes ... nothing. At least, nothing you can see. Cummins's southwest division manager, Mark Karrasch, challenges us to wipe a handkerchief inside the pipe. Luckily for him, there's no easy way to reach into the 13-foot-high mouth, but looking up, we can still see the glint of freshly rolled steel from inside the tube. It's pretty dang clean in there. A further federal cut in tailpipe soot is scheduled for 2010, when trucks will also be required to have onboard diagnostics, an emissions-system safeguard mandatory since 1988 on the vehicles you and I drive.

Wal-Mart, which operates the largest Class 8 fleet, has 200 ProStars on order. None will look like this one. Film Vehicle Services, a Los Angeles-based movie-support and vehicle-logistics company, striped its truck in blue and orange to a custom design by hot-rod czar Chip Foose. This ProStar has a six-foot-high sleeper cabin (the smaller, nonsleepers are called "day cabs") with a double bed, drawers, tables, and airliner-like overhead compartments.

On our top-of-the-line Limited, the dash is swathed in faux wood and accented by white-face gauges with chrome trim. The battery of rocker switches would be mysterious to a car owner: "Slide 5th wheel" moves the pie-plate-shaped hitch forward and back to adjust the tongue weight, and "dump susp" fully deflates the rear air suspension so the tail can stop under trailers and hook up. A digital screen gives drivers system-status and navigation info (it can direct them to the cheapest diesel fuel, too), and the truck is wired by satellite to headquarters so that fleet managers can see where it is and what it's doing.

During rest periods, long-haul drivers tend to leave their trucks idling to keep the A/C blowing and appliances running, burning about one gallon of diesel fuel per hour. No longer. Currently, 15 states have laws restricting truck idling to between two and 10 minutes, and more are being legislated. The ProStar's optional Cummins ComfortGuard auxiliary power unit, mounted outside the frame just ahead of the right rear tires, powers cabin electrics and a separate A/C unit with a two-cylinder Kubota diesel generator. It burns 75 percent less fuel per hour.

Cheese grits? We'll have the yogurt and granola plate, please.

In Pictures: 2007 International Prostar Limited

VEHICLE TYPE: front-engine, rear-wheel-drive, 2-passenger, 2-door 6x4 Class 8 tractor

PRICE AS TESTED: $186,240 (base price: $147,090)

TRANSMISSION: 13-speed manual

ENGINE TYPE: turbocharged and intercooled DOHC 24-valve diesel inline-6, iron block and head, direct fuel injection

Displacement: 912 cu in, 14,948cc

Power (SAE net): 450 bhp @ 1800 rpm

Torque (SAE net): 1550 lb-ft @ 1200 rpm

DIMENSIONS:

Wheelbase: 232.0 in Length: 332.0 in Width: 98.0 in Height: 156.0 in

Curb weight: 20,680 lb

C/D TEST RESULTS (unladen):

Zero to 60 mph: 24.2 sec

Zero to 80 mph: 41.6 sec

Street start, 5-60 mph: 23.1 sec

Standing ¼-mile: 24.9 sec @ 61 mph

Top speed (governor limited): 89 mph

Braking, 70-0 mph: 374 ft

Fuel economy (with 60,000-pound trailer):

Typical cruising: 8 mpg

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